A railroad vehicle has a motor that drives the vehicle and a vehicle control device that receives power from an overhead line and converts the received power to a required voltage or current to supply the power to the motor. Voltage or current conversion in the vehicle control device is mainly performed by an inverter device. For example, a three-phase alternating current (AC) output from the inverter device is supplied to the motor.
When a malfunction such as breaking of a command line for driving the inverter device or an open phase of the three-phase AC output from the inverter device occurs, the motor cannot be driven normally. Accordingly, prompt detection of a malfunction such as the open phase particularly in a low speed area of the vehicle is demanded.